<!DOCTYPE html>
<html>

<head>
    <style>
        p,
        div {
            margin: 5px;
            padding: 5px;
        }

        .border {
            border: 2px solid red;
        }

        .background {
            background: yellow;
        }

        .left,
        .right {
            width: 45%;
            float: left;
        }

        .right {
            margin-left: 3%;
        }
    </style>
    <script src="http://code.jquery.com/jquery-latest.js"> </script>
</head>

<body>

    <div class="left">
        <p><strong>Before <code>addBack()</code></strong></p>
        <div class="before-addback">
            <p>First Paragraph</p>
            <p>Second Paragraph</p>
        </div>
    </div>
    <div class="right">
        <p><strong>After <code>addBack()</code></strong></p>
        <div class="after-addback">
            <p>First Paragraph</p>
            <p>Second Paragraph</p>
        </div>
    </div>

    <script>
        $("div.left, div.right").find("div, div > p").addClass("border");

        // First Example
        $("div.before-addback").find("p").addClass("background");

        // Second Example
        $("div.after-addback").find("p").addBack().addClass("background");

    </script>

</body>

</html>